1. Field of the Invention
The present invention relates to a thermally developable photosensitive material. More specifically, the invention relates to a thermally developable photosensitive material which exhibits high sensitivity and excellent blue black image tone as well as has good photographic performance and good image storability.
2. Description of the Related Art
In recent years, in the fields of films for medical diagnosis and photographic films for plate-making, it has been strongly desired, from the standpoints of environmental protection and space-saving, to reduce the volume of processing waste fluids. Thus, there is a need for technologies relating to thermally developable photosensitive materials (heat development-type photosensitive materials), as films for medical diagnosis or photographic films for plate-making which can be efficiently exposed by a laser image setter or a laser imager to form clear black images having high resolution and sharpness. These thermally developable photosensitive materials are advantageous in providing customers with a thermal processing system that does not need liquid-type processing solutions, and which is simple and not harmful to the environment.
There is also a need for the same technologies in the field of ordinary image forming materials. In particular in the field of medical diagnosis, which requires detail depiction, high quality images excellent in sharpness and graininess are needed and blue black image tone is desired in view of diagnosing readiness. Currently, various types of hard copy systems using pigments and dyes, for example, ink jet printers and electrophotographic systems are widely used as the ordinary imaging system. However, satisfactory systems for outputting images for use in medical diagnosis have never been developed.
On the other hand, thermally developable image forming systems using organic silver salts are described, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075, and in xe2x80x9cThermally Processed Silver Systems (Imaging Processes and Materials)xe2x80x9d written by D. Klosterboer, Neblette, 8th Ed., edited by J. Sturge, V. Walworth and A. Shepp, Chap. 9, p. 279, 1989. In general, thermally developable photosensitive materials have a photosensitive layer (image-forming layer) produced by dispersing a catalytically active amount of a photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., organic silver salt), and optionally a toning agent for adjusting silver color tone in a binder matrix. Thermally developable photosensitive materials of this type are, after having been imagewise exposed, heated to an elevated temperature (for example, at 80xc2x0 C. or higher) to form black silver images through redox reaction between a reducible silver salt (serving as an oxidizing agent) and a reducing agent. The redox reaction is accelerated by catalytic action of latent images which have been formed on silver halides exposed. Therefore, the black silver images are formed in the exposed area. This technique is disclosed in many references, such as U.S. Pat. No. 2,910,377 and JP-B No.43-4924.
Thermally developable photosensitive materials do not require processing agents and do not discharge a large amount of wastes, whereby the materials have widely spread in the market as a good system to reduce burden on environment, which is currently a matter of concern. In particular, images used for medical diagnosis are required to achieve detail depiction to produce high quality images which have excellent sharpness and graininess. In addition, in view of readiness in diagnosing, blue black image tone is preferred in the field of medical diagnosis. From the foregoing, in the field of medical diagnosis, there have been a demand to produce thermally developable photosensitive materials which fulfill the requirements of exhibiting low fog, good storability, high sensitivity, high maximum density (Dmax) and excellent silver color tone, further has reduced dependency on temperature and humidity conditions during development, and hence are most suitable for medically diagnostic imaging.
In view of the prior art problems stated above, it is an object of the present invention to provide a thermally developable photosensitive material which exhibits low fog, good storability, high sensitivity, high maximum density (Dmax) and excellent silver color tone, and further has reduced dependency on temperature and humidity conditions during development, and thus is most suitable for medically diagnostic imaging.
The inventors conducted extensive researches and found that by selectively combining specific components to form an image-forming layer, thermally developable photosensitive materials exerting desired effects can be provided, thereby accomplishing the present invention.
That is, the present invention provides a thermally developable photosensitive material including a support and an image-forming layer disposed on one surface of the support, the image-forming layer containing a non-photosensitive organic silver salt, a photosensitive silver halide, a reducing agent for reducing silver ions, a binder and a compound represented by the following formula (I), wherein after the material is exposed and thermally developed at 121xc2x0 C. for 24 seconds, at least 90% of the developed silver is in contact with the photosensitive silver halide grains after development;
(X"Parenclosest"k"Parenopenst"L"Parenclosest"m"Parenopenst"Axe2x80x94B)nxe2x80x83xe2x80x83Formula (I)
wherein X represents a silver halide-adsorbing group or light-absorbing group having at least one atom of N, S, P, Se and Te; L represents a (k+n)-valent linking group having at least one atom of C, N, S and O; A represents an electron-donating group, B represents a leaving group or a hydrogen atom, and after the compound represented by formula (I) is oxidized, (Axe2x80x94B) is eliminated, or eliminated and further deprotonated to form a radical Axe2x80x2; and k falls between 0 and 3; m represents 0 or 1; n represents 1 or 2, with a proviso that if k=0 and n=1, then m=0.
The phrase xe2x80x9cfalling between xcx9c and xcx9cxe2x80x9d as used herein includes both upper and lower limits of a given numerical range.